Vestibular stimulation device

ABSTRACT

A vestibular stimulation array is disclosed having one or more separate electrode arrays each operatively adapted for implantation in a semicircular canal of the vestibular system, wherein each separate electrode array is dimensioned and constructed so that so that residual vestibular function is preserved. In particular, the electrode arrays are dimensioned such that the membranous labyrinth is not substantially compressed. Furthermore, the electrode array has a stop portion to limit insertion of the electrode array into the semi-circular canal and is stiff enough to avoid damage to the anatomical structures.

TECHNICAL FIELD

The present invention relates to devices for stimulation of thevestibular system.

BACKGROUND TO THE INVENTION

The vestibular system is a portion of the inner ear which enables thesensation of angular and linear motion. Neural signals corresponding tothis sensed motion are used by the brain to assist in a variety ofprocesses including balance and determining orientation, and in relatedmotor activities such as walking, standing, and visual orientation. Thevestibular system includes the three semicircular canals and theotolithic organs. Various abnormalities of the vestibular system areknown, and in severe cases they can result in significant disability forthose so afflicted. In older persons, the loss of stability attendantupon vestibular dysfunction can lead to a greatly increased likelihoodof a fall, and consequent loss of independence and mobility.

Ménière's disease is an abnormality of the vestibular system whichaffects approximately 1 in 2000 people worldwide. Ménière's has typicalsymptoms including periodic episodes of rotary vertigo or dizziness;fluctuating, progressive, unilateral or bilateral hearing loss;unilateral or bilateral tinnitus; and a sensation of fullness orpressure in one or both ears. It commonly begins with one symptom, andprogresses to others. The symptoms of Ménière's are highly variablebetween patients, and it is relatively difficult to diagnose withcertainty.

Approximately 85% of affected people can be treated with measures suchas medication, dietary changes, lifestyle changes, or behavioraltherapy. However, the remaining 15% are not assisted sufficiently bythese measures, and typically turn to one of a variety of surgicalprocedures, all of which have significant downsides.

It has been proposed to provide a vestibular stimulator using electricalstimulation in order to treat vestibular disease. U.S. Pat. No.6,314,324 discloses a vestibular stimulation device, using eitherelectrodes placed externally, or implanted neural stimulationelectrodes. U.S. Pat. No. 7,225,028 to Santina et al discloses a dualcochlear and vestibular stimulator.

It is an object of the present invention to provide an electrode arraysuitable for implantation within one or more semicircular canals of auser, so as to facilitate vestibular stimulation.

SUMMARY OF THE INVENTION

In a broad form, the present invention proposes a vestibular electrodearray structure, with the electrode arrays being constructed so thateach array will fit within one of the semicircular canals whilesubstantially preserving the existing rotational sensitivity of thesemicircular canal.

According to one aspect, the present invention provides a vestibularstimulation array, including one or more separate electrode arrays eachoperatively adapted for implantation in a semicircular canal, whereineach separate array is dimensioned and constructed so that the residualvestibular function is preserved.

In a preferred form, the array is dimensioned and constructed so that itmay be inserted within one of the canals without substantiallycompressing the membranous labyrinth.

The present invention also encompasses a vestibular stimulation deviceincorporating such an array.

According to another aspect, the present invention provides a method ofvestibular stimulation, wherein a vestibular stimulation array isimplanted into one or more of a user's semicircular canals, said arraybeing dimensioned and constructed so as to be inserted into asemicircular canal whilst still preserving residual vestibular functionand, preferably, without substantially compressing the membranouslabyrinth, said array being adapted to deliver electrical stimuli.

According to another aspect, the present invention provides a method ofoperatively positioning a vestibular stimulation electrode array, thearray being connected to a stimulation device adapted to measure neuralresponses to electrical stimuli, wherein the electrode array ispositioned in an estimated position, the stimulation device is operatedso as to produce stimuli from the array, and the neural response to saidstimuli measured, the process being repeated if required at differentpositions, so that the array is positioned at the position where themost desirable neural response is obtained.

According to another aspect, the present invention provides a vestibularstimulation array, including a body, the body being formed as a basesection branching into three separate canal arrays, each canal arrayincluding an insertable portion adapted for placement into asemicircular canal, each insertable portion including at least threestimulating electrodes, each of said electrodes being adapted toselectively deliver electrical stimulation, wherein the insertableportion has a diameter of less than about 150 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will now be describedwith reference to the accompanying figures, in which:

FIG. 1 is a general schematic illustration of the anatomical structuresof the vestibular system;

FIG. 2 is a more detailed illustration of the semicircular canals andrelated structures;

FIG. 3 is a schematic view of one implementation of an array accordingto the present invention;

FIG. 4 is a more detailed view of the implementation of FIG. 3;

FIG. 5 is a detailed view of the implementation of FIG. 3, including twoalternative electrode array structures;

FIG. 6 is a photograph of a device according to FIG. 5;

FIG. 7 is a view, partly in section, showing an array and a conceptualview of its preferred operative position and placement;

FIG. 8 is a schematic view of the implanted arrays; and

FIG. 9 is an illustration showing appropriate openings for insertingelectrode arrays into the semicircular canals.

DETAILED DESCRIPTION

The present invention will be described with reference to a particularillustrative example, which is a device intended for use in a vestibularstimulation system. The present invention is applicable to a system withimplanted components, powered and controlled from an external device, orto a fully implanted system, with a remote control or similar device. Itmay be incorporated with a cochlear implant or other hearing prosthesis,or be a stand alone device. It will be appreciated that the presentimplementation is described for illustrative purposes, and its featuresare not intended to be limitative of the scope of the present invention.Many variations and additions are possible within the scope of thepresent invention.

FIG. 1 illustrates the structures of the inner ear, with particularreference to the vestibular system 100. The three semi-circular canals102 are shown, each being arranged more or less orthogonal to eachother. Each canal is filled with endolymph fluid, and upon rotation ofthe head with a component of motion in the appropriate direction, fluidis caused to move within the canal. At the base of each canal is theampula 104 and the related crista 106. Within the crista 106 is thecupula 108 which contains hair bundles 110 connected to hair cells 112,and in turn to nerve fibres 114. When the fluid moves, the hair cells112 are stimulated, and produce a corresponding neural signal.

FIG. 2 illustrates in more detail the location and orientation of thevestibular labyrinth relative to cranial nerves VII and VIII andselected structures of the inner and middle ear. Illustrated are Nervusvestibularis 1, Nervus cochlearis 2, Nervus intermediofacialis 3,Ganglion geniculi 4, Chorda tympani 5, Cochlea 6, semicircular canals 7,Malleus 8, tympani 9, and ear canal 10. The illustrative embodimentwhich will be described is intended to be used in a relatively simple,constant stimulation system. This is intended to be operable by a userwhen they determine that they have symptoms indicating the onset of anattack, or alternatively in a preventative mode, in which the device isoperated to prevent the onset of an attack. However, it is envisagedthat the system could be implemented in a manner which is connected to amonitor that automatically enables/disables stimulation dependant onearly indicators of an attack. In another alternative, the system couldbe operated in constant “on” mode to maintain a manageable level ofvestibular function in cases of severe vestibular dysfunction. Directelectrical stimulation of the vestibular system by implanting anelectrode array atraumatically within one or more semicircular canalsprovides an alternative to other available medical or surgicalinterventions.

The proposed implementation consists of an external processor; transmitcoil (transcutaneous link); implant; electrode arrays; and remotecontrol or other activation device. For the purpose of treatingMénière's disease, one or more of the electrodes would be electricallystimulated to simulate the absent spontaneous neural activity. It willbe appreciated that other implementations, for example a fully implantedsystem, are possible.

One suitable implementation is shown in FIGS. 4, 5 and 6. Thestimulation device 40, and associated external power supply/stimulationcontroller, is a conventional cochlear implant stimulator device andexternal speech processor (not shown), with a customised electrode array(the latter will be discussed further below). This stimulator deviceaccording to this implementation is the Freedom receiver/stimulatorunit, available commercially from Cochlear Limited. The speech processorand associated stimulation system is capable of much more sophisticatedstimulation than is required for the present application, at least in sofar as a simple implementation is concerned.

For the purposes of understanding the cochlear implant stimulationsystem, in this case being used for vestibular stimulation, thefollowing explanation is provided. However, the reader should review thecommercially available cochlear stimulation devices if further detail isrequired.

Cochlear prostheses generally include an external, wearable control unitthat determines a pattern of electrical stimulation that is provided toan implanted stimulator unit containing active circuitry in a hermeticenclosure. Electrical stimuli are delivered through electrodes toprovide electrical stimulation of auditory nerve cells.

Once implanted, the electrodes of the electrode array receivestimulation signals from a stimulator unit. The stimulator unit istypically electrically connected to the electrode array by an electricallead. The stimulator unit is positioned within a housing that isimplantable within the patient, and is typically implanted within arecess in the bone behind the ear posterior to the mastoid. Whenimplanted, the housing preferably contains, in addition to thestimulator unit, a receiver unit adapted to receive signals from acontroller. The controller is, in this example, mounted external to thebody behind the pinna of the patient such that signals are transmittedtranscutaneously through the skin of the patient.

The signals travel from the controller to the receiver unit and viceversa. The receiver unit includes a receiver antenna, such as an antennacoil, adapted to receive radio frequency (RF) signals from acorresponding transmitter antenna, such as an antenna coil, wornexternally of the body. The radio frequency signals may comprisefrequency modulated (FM) signals, but could alternatively be modulatedin any suitable way, using, amplitude, frequency or phase, using eitheranalog or digital techniques. In general, the modulation should bechosen in order to maximise both the data and power efficiency of thelink. It should be appreciated that the receiver antenna may alsotransmit signals, and that the transmitter antenna may receive suchsignals. The transmitter antenna coil is preferably held in positionadjacent the implanted location of the receiver antenna coil by way ofrespective attractive magnets (not shown) mounted centrally in, or atsome other position relative to, the coils.

The external controller in this example includes a processor (not shown)adapted to encode a suitable stimulation signal, for example in responseto the device being turned on by the user. Such a signal would includedata defining, for example, the mode of stimulation, current level, andwhich electrodes are to be stimulated. As the present inventioncontemplates the use of three separate electrode arrays, the stimulationmay occur on more than one array simultaneously, or alternatively,sequentially. The encoded sequence is transferred to the implantedreceiver/stimulator unit using the transmitter and receiver antennae.The implanted receiver/stimulator unit demodulates the signals andallocates the electrical pulses to the appropriate electrode. Theexternal controller may further include a power supply (not shown). Thepower supply may comprise one or more rechargeable batteries. Thetransmitter and receiver antennae are used to provide power viatranscutaneous induction to the implanted receiver/stimulator unit andthe electrode array.

It is contemplated that the implanted arrays should be adapted todeliver both monopolar and bipolar stimulation. Bipolar stimulationoccurs when a current flows from one electrode to another electrode ofthe same array, that is, in the same canal. Monopolar stimulation occurswhen current flows between an electrode within the canal and anelectrode external to the canal, for example a separate implantedelectrode external to the canal. Depending on the stimulation currentrequired to elicit a response bipolar may be advantageous in minimizinginteraction with adjacent semicircular canals. At least two channels,typically one intracanal and one inter canal, are also required forNeural Response Telemetry which has been shown to be important duringsurgery for electrode placement.

When there is no movement, the normal vestibular system generatesconstant regular activity, i.e., the neurons in the semicircular canalfire at a constant rate. Without limitation to the present invention,Ménière's disease is believed to cause an increase in the pressure ofthe endolymph in the semicircular canals. This in turn causes theneurons to cease their regular firing.

The objective of stimulation is to simulate this constant firing throughdelivery of electrically evoked afferent activity. This may, accordingto the present implementation, be unmodulated. However it iscontemplated that other implementations may be modulated, for example infrequency or amplitude, in order to provide more complex user percepts.Clinically a stimulation method would be chosen so that it delivers therequired stimulation (and desired percept); provides no interferencefrom one canal to another; and operates at the lowest level of power.The electrical stimuli required are generally of a much lower complexityand at lower rate pulse trains than for auditory stimulation. Forexample, the electrical stimuli may be provided as biphasic pulses at100-200 Hz, 400 μs phase width, 8 μs phase gap and currents of between20-100 uA. These figures are indicative only, and implementations mayuse other parameters.

A particular feature of implementations of the present invention is thatan electrode array is intended to be inserted into each of thesemi-circular canals whilst preserving any residual vestibular function.This is achieved using a suitable dimension, for example for a circulararray, a diameter less than 150 microns. Other specific characteristics,relating to length, a stopper to limit penetration, and stiffness assistin this objective, as will be explained further below.

The principal issue with preserving existing function is to avoid damageto existing structures, and the present invention contemplates electrodedesigns intended to achieve this. Whilst the implementation describeduses a diameter limitation approach and an electrode array similar instructure to a cochlear implant device, it will be appreciated that thisresult may be achieved by selection of materials, alternative shapes forthe array body and electrodes, and other mechanisms, all of which areencompassed within the general inventive scope. For example, the arraymay have a special coating or be formed from a special material toassist in insertion. Specific electrode designs, in either or bothmechanical and structural feature, or in the electrical structure, mayassist in achieving the objective. Similar structures, materials andapproaches could be used as for cochlear electrode arrays, especiallyhybrid arrays intended to preserve existing auditory function. The arraycould, for example, be drug eluting in order to minimise reaction toforeign bodies, or to reduce the risk of post-implantation infection.

According to the preferred implementation, a number of small electrodearrays for surgical placement between the bony labyrinth and themembranous labyrinth of each semicircular canal (superior, posterior andlateral) of the vestibular labyrinth. Referring to FIG. 3, the electrodearray 20 consists of an electrode lead 29 which trifurcates at junction28 into three leads 21, 22, 23, each intended for one of thesemicircular canals. Each lead 21, 22, 23 terminates in a respectiveelectrode array 24, 25, 26, intended for insertion into one of thesemicircular canals. Each array (illustratively 26) has three electrodes31, 32, 33 for applying stimulation. The array further includes astiffening member to provide the necessary mechanical characteristics,as will be discussed further below.

The aim of the vestibular electrodes is to provide an electricalinterface to the vestibular periphery without damaging or destroyingresidual vestibular function, in order to restore a level of vestibularfunction for people with disorders such as Ménière's disease.

The electrode array is designed for vestibular stimulation, and has anumber of special features.

As can be seen from FIGS. 3, 4 and 5, the array 20 allows the surgicalplacement of three individual electrode arrays 24, 25, 26 to either one,two or all semicircular canals. The trifurcated lead allows for ease ofsurgical placement by providing a single lead 29 which branches intothree leads 21, 22, 23 and electrode arrays 24, 25, 26 that can beindividually implanted. The trifurcated structure improves leadreliability (impact, fatigue, stress, etc), compared to having threeseparate leads exiting the stimulator, and simplifies the feedthroughstructure from the stimulator. In the event that explantation isrequired, this structure reduces the time required and simplifies thesurgical removal of one or all electrodes, or the entire device,compared to having three separate leads exiting the stimulator.

FIGS. 4 and 5 illustrate detailed views of the electrode array 26,designated 26A and 26B in FIGS. 4 and 5. The length A of each electrodearray is preferably 2.5 mm. An alternative array is illustrated, with alength A, or insertion depth, of 1.7 mm. This is illustrated by theelectrode array of 26B appearing shorter than that of 26A. In thepreferred form, the electrode array span B is 1.15 mm, the individualelectrode length C is 0.25 mm across and the electrode gap D is 0.2 mm.The lead before the insertion part has a larger diameter E,illustratively 0.64 mm, as compared to the insertion part F, which is0.15 mm in diameter. This can also be seen in FIG. 7. The electrodearray begins a distance G, which is preferably 1 mm, from the end of thelarger diameter lead. An embedded stiffener 34 helps to keep theelectrode array rigid.

The illustrated arrangement of electrode arrays allows for the placementof one electrode array in one semicircular canal, with the remainingelectrode arrays placed safely within the mastoidectomy cavity forpossible future implantation in the remaining semicircular canals. Inthis case, only the implanted array is used for stimulation. Theremaining electrode arrays could also be used for possible otolithicstimulation via implantation of the vestibule, possibly via a round oroval window approach, or via the common crus.

FIG. 6 shows one implementation of the invention, using a conventionalcochlear stimulation device 40. The device includes the trifurcated lead20, as well as a reference electrode 45. The detail shows an enlargedview of the array, showing the electrodes 31, 32, 33.

FIG. 9 illustrates suitable surgical openings 55, 55A, 55B in theposterior 51, superior 51B and lateral 51A semi-circular canal, throughwhich the electrode array 26 may be implanted. In each case, therespective ampulla 50, 50A, 50B can be seen. FIG. 8 shows thearrangement post-implantation, with the posterior semicircular canal(Psc) 51, the lateral semicircular canal (Lsc) 51A and the superiorsemicircular canal (Ssc) 51B shown only in their general positionsbehind a tissue wall, although the surgical openings 55, 55A and 55B andthe leads 21, 22 and 23 are shown extending through their respectivesurgical openings.

FIG. 7 shows one of the arrays being inserted into the opening, and itscorrect placement. The array 26 is inserted within the canal, proximateto the ampulla 50, between the bony labyrinth 52 and the membranouslabyrinth 53. Studies have indicated that a better response tostimulation is achieved if the electrodes are proximate to the ampulla,however, it is generally considered important that the electrodes do notcontact the ampulla. FIG. 7 also illustrates the appropriate fit of theelectrode array—once in position, as can be seen in the post insertiondrawing, the electrode array 26 lies next to, but not compressing orpenetrating the membranous labyrinth 53, with duct 54 intact. Thediameter of the array is selected to be sufficiently small to achievethis.

It is preferred that the insertion depth is controlled, so as to preventthe potential for damage to the ampulla. This has been identified fromanatomical studies as 2-3 mm. In a preferred form, the part of the arrayfor insertion is 2.5 mm long, and a stopper is provided to preventfurther insertion. This may suitably take the form of an increaseddiameter of the lead distal to the electrode array itself. Thesefeatures can be seen from FIGS. 6 and 7.

A small piece of fascia may be placed around the electrode array distalto the stopper, so that sealing of the ‘canalostomy’ can be promoted. Itis important to minimise the exposure of perilymph. A platinum collar ormesh material could be incorporated to promote sealing.

The trifurcated lead is preferably between 15-45 mm, suitably 30 mm, inlength. This has been identified via animal studies and cadaver studiesas providing appropriate access and fixation. The placement of thetrifurcated parts at suitable mutual angles, for example 20-40°,facilitates surgical placement into each semicircular canal.

It is desirable that the array have sufficient stiffness and dynamicssuch that the electrode can be placed reliably within the labyrinth. Theelectrode array according to this implementation incorporates astiffening member with unique characteristics, allowing the electrodearray to be of the required diameter, yet of sufficient stiffness toinsert to the desired depth between the bony labyrinth and themembranous labyrinth of each semicircular canal. The array should have astiffness allowing a single stroke atraumatic insertion to the requireddepth in the canal. On the other hand, it must also have sufficientflexibility to deflect and avoid damage to the delicate anatomicalstructures. If the array is too stiff, it would be more prone to pierceor compress the delicate anatomical structures: if it is too soft orflexible, the electrode array may buckle and deform during insertion,and thereby cause trauma.

It has been determined by surgical trials, on animals and cadavers, thata suitable stiffness is comparable to 0.12 mm platinum wire. However, itwill be appreciated that other values may be used in otherimplementations, noting the considerations mentioned above. It wouldalso be possible to use a removable stiffening or insertion member, orto have variable flexibility.

The array must be operatively placed within the labyrinth whilstpreserving vestibular function/sensitivity, but providing robustelectrical stimulation of the vestibular periphery. It should allow forthe use of soft surgery, including a small labyrinthotomy to gain accessto and to preserve the membranous canal. The electrode array shouldinsert between the bony labyrinth and the membranous labyrinth, withoutcompressing the membranous labyrinth. It is preferred that the electrodearray, or at least the part for insertion into the canal, has a diameterof 150 microns or less. This has been identified via cadaver and animalstudies as optimal.

It is preferred that each array has a sufficient number of electrodes topermit both monopolar and bipolar stimulation, as well as to providesufficient redundancy in the event of individual electrode failure. Itis preferred that a suitable reference electrode is also provided as areturn path for monopolar stimulation. A minimum of three electrodes ineach array is preferred, as illustrated, however, a larger or smallernumber of electrodes may be use to provide the same effect or to providea subset of the above capabilities. It may be possible to haveadditional electrodes, however, appropriate criteria for electrodedimensions and charge density characteristics discussed elsewhere shouldbe met. The electrodes also facilitate NRT measurements to optimiseplacement during implantation.

Initial implantation away from the ampulla of the lateral canal producedsmall responses at high current thresholds that were not in the canalplane. These were associated with limited dynamic range (current limitsand recruitment of facial nerves were a problem).

Revision of the electrode placement closer to the ampulla producedthresholds an order of magnitude lower, and no cross talk to the facialnerve.

Precise electrode placement near the ampullae of the semicircular canalsis critical for robust activation of the vestibular system, asdetermined by eye movements in response to electrical stimulation andthe ocular reflex. The ocular reflex is a function of vestibularstimulation. Electrode placement that is too shallow, or too deep,results in weak or absent vestibular responses. Fortunately a reliableintraoperative tool for assisting in optimal electrode placement hasbeen developed. Animal trials have demonstrated that, like the cochlearnerve, the vestibular afferents produce an electrically-evoked compoundaction potential (ECAP) that can be recorded from the implant usingstandard clinical Neural Response Telemetry software. When theseresponses can be recorded, robust electrically-evoked eye movements areobtained. When the responses cannot be recorded, no or minimal eyemovements are obtained from stimulation.

Correctly positioned electrodes produce large, higher velocity nystagmiceye movements, slow phase velocities that scale with the frequency ofstimulation, slow phase velocities that scale with the stimulus current,velocities greater than 50 degrees/s and amplitudes great than 10degrees.

Whilst the present invention has been described with reference to asimple form of vestibular stimulation, it will be appreciated that thepresent invention could be used in conjunction with a more complexsystem. It could be applied, for example, with a vestibular prosthesiswhich operates to replicate impaired vestibular function using sensorsfor orientation and/or acceleration and corresponding electricalstimuli. Such systems may be of assistance in treating conditions suchas bilateral vestibular hypofunction or areflexia and unilaterallabyrinthitis.

1.-19. (canceled)
 20. A vestibular system stimulation array, comprising:at least one electrode array configured to be implanted in asemicircular canal of the vestibular system, and further configured toapply electrical stimulation to the vestibular system while implanted inthe semicircular canal, wherein the at least one electrode array isdimensioned such that residual vestibular function of the semicircularcanal in which the at least one electrode array is implanted isretained, and wherein the electrode array comprises a stiffener embeddedin the electrode array.
 21. The stimulation array of claim 20, whereinthe at least one electrode array and the embedded stiffener has astiffness comparable to a stiffness of a 0.12 mm platinum wire.
 22. Thestimulation array of claim 20, wherein: the at least one electrode arrayis configured to be implanted in the semicircular canal such that theelectrode array does not substantially compress a membranous labyrinthof the semicircular canal.
 23. The stimulation array of claim 20,further comprising a stop to prevent over insertion of the electrodearray into the semicircular canal.
 24. The stimulation array of claim23, wherein the stop is disposed at a distance greater than 2.5 mm froma distal end of the electrode array.
 25. The stimulation array of claim24, wherein the electrode array span is about 1.15 mm.
 26. Thestimulation array of claim 20, wherein a diameter of the electrode arrayis about 150 microns.
 27. The stimulation array of claim 20, wherein theelectrode array is configured for operable insertion between a bonylabyrinth and a membranous labyrinth of the vestibular system.
 28. Thestimulation array of claim 20, wherein the electrode array is configuredfor operable insertion between a bony labyrinth and a membranouslabyrinth of the vestibular system such that the membranous labyrinth issubstantially uncompressed.
 29. A vestibular system stimulation array,comprising: at least two electrode arrays each configured to beimplanted in a semicircular canal of the vestibular system, wherein theat least two electrode arrays are configured to apply electricalstimulation to the vestibular system, and each of the at least twoelectrode arrays are dimensioned such that residual vestibular functionof a semicircular canal in which a corresponding electrode array isimplanted is retained, wherein each of the at least two electrode arrayscomprises a stiffness comparable to a stiffness of a 0.12 mm platinumwire.
 30. The stimulation array of claim 29, further comprising at leasttwo leads each connected to a respective one of the at least twoelectrode arrays.
 31. The stimulation array of claim 30, wherein therespective leads are part of a trifurcated lead assembly.
 32. Avestibular system stimulation array, comprising: at least one electrodearray configured to be implanted in a semicircular canal of thevestibular system, and further configured to apply electricalstimulation to the vestibular system while implanted in the semicircularcanal, wherein the at least one electrode array is dimensioned such thatresidual vestibular function of the semicircular canal in which the atleast one electrode array is implanted is retained, and wherein theelectrode array comprises a stiffness comparable to a stiffness of a0.12 mm platinum wire.
 33. The stimulation array of claim 32, furthercomprising a stiffener embedded in the at least one electrode array. 34.The stimulation array of claim 32, wherein a diameter of the electrodearray is about 150 microns.
 35. The stimulation array of claim 32,wherein the at least one electrode array is configured to be implantedin the semicircular canal such that the electrode array does notsubstantially compress a membranous labyrinth of the semicircular canal.36. The stimulation array of claim 32, further comprising a stop toprevent over insertion of the electrode array into the semicircularcanal.
 37. The stimulation array of claim 32, wherein the stop isdisposed at a distance greater than 2.5 mm from a distal end of theelectrode array.
 38. The stimulation array of claim 32, wherein theelectrode array span is about 1.15 mm.
 39. The stimulation array ofclaim 32, wherein a diameter of the electrode array is about 150microns.